How do I force iPad to display book covers from the icloud?

Book covers disappear: I have a large book collection (approx 1,500) and have used separate software (calibre) to ensure the book covers are correct. My books are stored in the cloud, however until recently they used to show all the covers on my iPad. The books now show generic covers. How do I force the iPad to show the covers (even if the actual books are still in the cloud). I’ve tried lots of different things that Gemini/ChatGPT recommend, but none of them have worked. Can anyone give me a solution that is guaranteed to fix this?

[Re-Titled by Moderator]